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You'll get a letter

If you don't file, you'll get a letter from the IRS saying it didn't receive your return. That letter could take anywhere from six to 18 months to arrive. "The IRS is working on real-time notification to ease and quicken the process," Riley said.

The IRS will ask if the taxpayer is deceased, if a return was filed but never arrived, or if one was never filed. In the last scenario, the IRS will tell you to file immediately.